Arrangement for deriving an adjustable partial voltage from an electric signal voltage



Aug. 27, 1963 N. A.'DE GlER 3,102,227 v v ARRANGEMENT FOR DERIVING AN ADJUSTABLE PARTIAL VOLTAGE FROM AN ELECTRIC SIGNAL VOLTAGE Filed Feb. 28, 1958 2 Sheets-Sheetl l ,i v lNvENTQR v l v N\ ARIE DEGIER Aug. 27, 1963 N. A. DE GIER 3,102,227

v ARRANGEMENT FOR DERIVING AN ADJUSTABLE PARTIAL VOLTAGE FROM ANYELECTRIC SIGNAL VOLTAGE vFiled Feb. 28, 1958 2 Sheets-Sheet 2 INVENTOR `mazo Am: DE Glen -AGENT ARRANGEMENT Fon DERIVING AN ADJUST- ABLE PARTIAL VOLTAGE FROM AN ELECTRIC SIGNAL VOLTAGE .Nico Arie de Gier, Eindhoven, Netherlands, assignor t North American Philips Company, Inc., New York, N.Y., a corporationof Delaware Filed Fears,19s8,ser.No.11s,3z2 l Claims-priority,application Netherlands Mar. 9, 1957 Claims. (Cl. 323-64) This .invention relates to an arrangement for deriving an adjustable partial voltage from an electric signal voltage supplied to the arrangement, which signal voltage 1s -supplied toa series Icombination of at least two impedlances, the partial voltage being taken from a part of this series combination.

Such. arrangements are frequently used ixr-electrical and electronic apparatus, for example, radio receivers, amplifiersand measuring apparatus, in which an adjust- "able part of a vgiven signal voltage must be transmitted. A well 'known use is the gain control in low-frequency amplifiers. To this end, use is generally made of a socalled resistance. potentiometer comprising an electric ,resistancev which isv provided on an insulating support and may take the form of a carbon layer or of a resistance wire wound on the support, over which an electrical .contact supported from a movable member can be adjustably displaced. Such potentiometers lsuffer from the disadvantage that theyare liable to crackling, that is to say, the output signal taken from one end of the resistance path and the movable contact contains an electrical noise owing toicontact phenomena.

It is van object of the present invention to provide an arrangement of the above-mentioned kind in which such contactnoise is completely avoided.

l. An arrangement in accordance with the invention is characterized in that the series combination includes a photo-resistance which is associated with a light source, means 'being' provided for adjustably'varying the irradiation of the photo-resistance by the light. The adjustment of the requiredratio between the partial voltage .and the signal voltage supplied'is obtained by optically varying the resistance of part of the series combination independently of the signal voltage. Consequently, all the junctions at which the applied signal voltage and/or the partial yvoltage is set up, are fixed and hence can be soldered. v i

In one embodiment of the arrangement in accordance withthe. invention, the adjustment of the irradiation of the photo-resistance is obtained by means of a member which'is arranged in the path of the luminous ux from `the lightsource to the photo-resistance so as to be displaceable at right angles thereto and which, according to its position, intercepts this luminous ux in a greater or lesser degree. This'member may be .designed in various manners. It may, for example, be an apertured mask or atransparentl member of continuously variable density, for example a photographic neutral wedge filter,

while use may also be made of a colour filter which at different points passes light of`a dierent colour.

In another embodiment of the arrangement according to the invention, the variable irradiation of the photoresistance 'is produced by means of an electric light source, means being provided for controlling the electrical energy supplied to the light source. K

In another design of the arrangement according to the invention, vthe arrangement contains a second photoresistance connected in series with the first photo-resistance. This second photo-resistance may be completely screened from irradiation so that it vacts as a resistance of fixed value in the series combination. In another embodiment of this design, a light source is associated ICC with this second photoresistance also, meansv being provided for adjustably varying theirradiation of this-second photo-resistance by the associated light source. Preferably, the means for adjustingy the irradiationl of they two photo-resista'nces are coupled to oneanotherso that the variation in the irradiation of`one photo-resistance is always opposite tothe variation inthe irradiation of the other photo-resistance. y

lt should be noted. thatan arrangement is known which contains two series-connected photo-resistances, the elec-- trical voltage being supplied through onefot. the photoresistances to the grid of a discharge tube the anode. circuit of which includes a relay switch. This arrangement is intended for use as a supervisoryy system, the

certain information to be transmitted, in the known arrangementv the electrical voltage impressed upon the series combination is set to a constant value whichis matched to the protective light beam. In the known arrangement, the light incident on the photo-resistances rcontains kthe information to be utilized. I

In order that the invention may readily be carried out, a number of embodiments thereof will' now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which.: l

FIG. l shows a first embodiment, and

FIG. 2 is a front elevation of a photo-resistance used in the arrangement shown in FIG. l.

- FIG. 3 is a cross-sectional view of a second embodiment, and v FIG. 4 is a developed view of `two cooperating masks used in this second embodiment.

FIG. 5 shows an embodiment which is highly suited to remote control.

FIGURES 6 and 7 show an embodiment in which the impedance of the series combination is substantially independent of the adjustment of the arrangement.

FIG. 8 is a front elevation of a multiple photoresistance which may be used in the arrangement shown in FIG. 7.

FIG. 9 shows an embodiment to be used for physiological gain control in low-frequency amplifiers.

In-the figures, the input terminals of the` arrangements are designated 1 and 2, the output terminals being designated 3 and 4. Anv electrical signal voltage V, is applied to the input terminals 1 and 2. This voltage at each instant contains certain information which is to be transmitted by the arrangement so that it appears in a voltsulphide, provision is made of two comb-shaped interlaced electrodes 8 and 9. One of these electrodes, which may consist of silver or conductive stannic oxide, is directly connected to the resistance 5, the other being directly connected to the input terminal 2 and the output terminal 4.

A electrical light'source lll, which may be a bicycle l of a displaceable mask having awcontinuouslyl variable headlight lamp, is associated with the photo-resistance 6. An iris diaphragm 11 is interposed between the, light source and the surface of the photo-resistance 6 upon which the electrodes 8 and 9 are provided. Adjustment ofthisdiaphragm by enlarging or diminishing a central aperture 12 enables `the surface area of the portion 13 (FIG. 2) of the'photo-resistance which is exposed to radiation from -the lamp 410 to be adjusted at wilt.- AWhen the aperture 12 is large, so that the entire photo-resistance 6 or at least the greater part lthereof isr irradiated,l

the electric-resistance of this photo-resistance is low,

' while with ya very small aperture 12 the electric resist-ance of the photo-resistance 6 is high. If this photo-resistance l isl a cadmium. sulphide disc having a ldiameter of 8.5 mms., the velectrodes 8 and 9 being spaced from -one another by 0.2 mm., the resistancevalue of the photo- 'resistance 6 can be adjusted by means of the diaphragm 11 from about 5 megohms to about'0.5 kilo-ohm.

This means that, with a value of the resistance 5 of,

for example, 0.5 MQ the value of the output voltage. Y across terminals 3 and 4 can'be varied roughly from nine tenths to one thousandth of the input voltage V1.

Since there are no movable electrical contacts in the input and output voltage eircuits,the occurrence of contact noise in the output voltage Vu isprevented.

In the figures referring to the embodiments described hereinafter, the component parts corresponding to those which sleeve at one end isprovided with a lampholder 35 in which al lamp 10 is centrally mounted. A secondV cylindrical sleeve 34vis mounted for rotation about its axis in the sleeve 32 so as to surroundthe lamp 10.

Between the lampl 10 and thephoto-resistance 6, the

density or constituting a` variable colour filter.- However, in the arrangement shown in FIG. 5 the luminous, flux is controlled in a 'different manner, whichis particularly suitable for remote controLv The. arrangement shown in f'FIG. 5 is distinguished from those shown in FIGURES l to 4 by the absence of a separate movable memberbetween the' lamp 10 and the photo-resistance 6 and bythe inclusion of a variable resistance 52 in asupply lead 50through whichthe lamp 10 is supplied from asource 51.`

The supply source 51 may be a supply transformer in a radio receiver or the like. The` adjustment of the variv able resistance 5 2, Which may be a cheap wire resistance or carbon resistance, determines the-luminous flux which strikes the photo-resistance 6 and 'hence the resistance value of ythis photo-resistance. This arrangement is particularly suited for remote gain control in sound repro.

ducingand/ or recording apparatus. The control resistance 52 can beconnected to the apparatus incorporating the remainder of the arrangement by means of a twoconductor cord of substantially arbitrary length. r[he arrangement shown in FIG. 5 is of advantage also when the control resistance .52 is located in the apparatus itself. In a radio receiver, -for example, the lseries combination of the resistanceS and the photo-resistance 6 can be'disposed in the immediate vicinity of the detector` and the sleeve 32 is provided with a substantially tear-shaped` 'another to a maximum extent, the overlapping part which shifts towards the aperture tails can begradually .'reduced. Thus', the angular position of the rotatable sleeveV 34 with respect to the stationary' sleeve 32 determines the luminous llux received bythe photo-resistance 6. Consequently, the angular positioning of the sleeve `34 determines the ratio between thef'output voltage, Vu

and -the input voltage V, similarlyf to the adjustment of the diaphragm 11 in the arrangement shown in FIG- URES 1 and 2.v v v- The shape of the apertures 36 and 37 is chosen so l that the resistance value of the photo-resistance 6 as a functionof the angular position ofthe sleeve 34 has a substantially logarithmic variation. By a suitable choice of the shapes of the apertures 36 and 37, substantially vany required form of the resistance curve ofthe photo'- resistance can be achieved.

While in the arrangements described hereinbefore the resistancevalue of the photo-resistance connected in the series combination is determined by an aperture in a mask, which aperture determines the light beam incident on the photo-resistance, in the arrangement according to FIG. .S it is not the'size of the light beam, `but the amount of light per .unit of surface of the photo-resistance which-is varied. Such can be obtained by the intcrposition between the lamp l0 and the photo-resistance 6 following first low-frequency amplifying stage, the control resistance 52 being mounted at a readily accessible point. This provides the advantage that the length ofthe conductors through which the low-frequency signal is transmitted can be keptnto a minimum without detracting from the operability.

In the arrangement shown in' FIG. 6, the resistance value of the photo-resistance 6 is also adjusted by controlling the electrical energy absorbed by thelamp 10.

However, this arrangement is distinguished from the preceding by the fact that `the fixed resistance 5 is replaced by a photo-resistance 60 with which is associated a second lamp 61 of the same kindas the lamp 10. A screen 63 prevents light from the lamp 10 from falling von the photoresistance "60 and light from a lamp 61 from falling on the photo-resistance 6. The lamps 10 vand 6l are seriesf connected to a Itransformer 64. In parallel with the two lamps 10 and 61 there is connected a potentiometer 65 of ythe usual kind, a movable contact 66 of which is elec-v trically connected to the midpoint of vthe series combination of the two lamps. In the highest position`(FIG. 6) of the contact 66, the lamp 61 is short-circuited while the lamp 10 has thefull voltage of the transformer 64 applied to it.y In the lowest position of the contact 66, this condition is reversed. When the adjustment of the contaet66 is changed, the resistance values of the photo-resistances 6 and 60 are changed in opposite'senses. Thus, the output voltage Vu across the terminals 3 and 4 can be varied through a range extending from a very slight fraction of the input voltage Vj to substantially the entirel input voltage.

control is effected by displacing a mask 70, which is pro- `vided with a rectangular aperture 71, parallel to the photo-resistances which are situated in the same plane behind the mask.v The two photo-resistances 6 and 60 both co-operate with a lamp 10 which through the aperture 7l irradiatcs a portion of cach of these photnJcsist- :mecs which is determined by the position nl' the mask 70. 'lhe ratio 0ll lite surface :trema ul the exposed purtion is determined by the position ot' the musk 70.

" example lcopper-activated cadmium` sulphide.'

The two photo-resistances 6 and y60 of the arrangement shown in FIG- 7 may form an integral structure.

FIG; 8 is a front elevation of such a structure. A photo- '-sensitive'layer/S, whichis coated on a support which is Anotshown'in-the drawing, `is-.providedwith-a number of parallel extending' electrode lines which are interconnected so asfto'torfmz three groupsl,l 82 yand-8 3. The

lines ofthe group 81 and those of the `group'83 are interlacedby lines of the-group 82. The lines of the group "f 81- are connected to the input-terminal 1, the lines of the group=82lfare connected to thev output terminal 3, =while the li es of the group 83 are connected to rthe inputv l ltei'min'al Zlwliich is also the output terminal 4. The part t .of the" resistance structure which in the position of the mask 70-shownxin FIG. 7 is .exposed to light from the lamp 10, is shown in FIG. 8 by a rectangle `84 shown in broken lines.

A multiple photo-resistance as shown in FIG. 8 can be A:used to replace the resistance together with `the photoresistance 6 of the embodiments shown in FIGURES l, `3 and 5; In this event, part of ther photo-resistance, for example-the part containing the. electrode lines 81, must Vbe permanently screened from lightv from the lamp 10,

for example, by coating it with black. lacquer.

4In ,all the embodiments described hereinbefore, the outf Y put Avoltage Vuais taken from 'the photo-resistance ,-6 one end of which is directly connected to the input terminal -2.

" Itwill be .appreciatedthat a voltage produced across other 'p'ointsuof 'the circuit arrangement may alternatively be used as the output voltage., T hus, the voltageacrossrthe wterminals 1y and 3 cangbe ytaken as the output voltage. f

`,The resistance 5 can be replaced by a reactance, for

example a capacitor, or vby a series combinationl of atleast f1 two 'impedaneesl vIn thislatter case, the output voltage canbe taken from `one of :these impedances.

When the irradiation on the photo-resistances v93 and 94 is comparatively intense, so that their resistance values are low, the low and hig'hlfrequencies are more pronounced in the resultingjlow output voltage than if kthey .are exposed to light of lesser intensity, in which event lthe output voltage is higher.

Throughout this specification, use `is'kmade ofthe terms vflight source, luminous flux' and lirradiatior'il'y Where we n are concerned with radiation .for modifying ytheelectrical resistance `of a photo-resistance, 'the lterm` light should not bel understood to be limited to visiblev radiation. kFor v the end in View, use can also be made o radiation Outside the visible part offthe spectrum, for example ultravioletv and infrared radiations, provided :that the photorcsistance'or -resistances are sensitive to ysuch radiation.

Obviously, in an arrangement'in accordance with ythe invention, precautions must, if required; beitaken Lto :ex-

clude` any .undesirable radiation `which `mayv affect the photo-resistance ofthe photo-resistances, Kor example by mounting the photo-resistance or photo-resistances and the source of radiation lin .a :separate housing, similarly to what has been vdescribed with reference to FIG. 2.

What is claimed is: e .1.. .A circuitarrangement comprising a'source of time varying intelligence signal voltage, first andfsecond impedance elements connected in -series circuit arrangement,

atleastl one kof said impedance elements comprising a photosensitiveimpedance, means `for-impinging radiations y.upon said photosensitive impedance, means for varying the intensity of radiations impinging on said photosensitive impedance independently of said source of intelligence signa-l l,thereby varying the impedancevalue 'of the l. said photosensitive impedance, 'means for aplying said w FIG..J9-shows-.an arrangement in accordance with the v of audio-frequency electric. signals. r

The audio-frequency input voltageis supplied, through terminalsl and 2, to the `series combination of a resistyinvention which is intended for physiological gain control ance 91', a'nsecond resistance 92 and a photo-resistance 93 whichffdrms anintegral-structure with a second photoresistance 94. vThe .two photo-resistances have combs shaped electrodes 95, 96 and 97, the latter being common 1 .toiboth photo-resistances.

Theseelectrodes are yprovided e on a disc pressed from a photo-sensitive substance, for

` a capacitor `98, thegelectrode 96 of the photo-resistance 94 v is connected tothejunction ofthe resistances 91 and' 92.

; Furthermore, a capacitorg99 is connected in parallel with the resistance 92. lThe; ouputterminals 3l and 4 are .directly connected to the'electrodes of the photo-'resistl By-means of a lamp '510, which may be lconnected t0 1a" transformer in a radio receiver,.anampliiier or other sound Aapparatus in which the arrangement is'included,

the-two photo-resistances 93,and 94 arevequally irradiated. The luminous flux 1.00 VStg-.'ikir'lg vthese photo-resistances can be-controlled bymeans which are not shown ,in the drawing. Thesemeans may consist of a displacea- .-ble mask rinterposed between the lamp 10 and the two photo-res,ist'ances or of a filter 'of locally varyingdensity oreolcnrr.vv Alternatively, use mayv be "made of means for controlling the supply of energy to the lamp 10. Em-

I. h'bodimentS-Df-.these meanshave already been described ,.wit.h:-l I 'i 4 f--Suitabl ce ',to, preceding examples. e ,y

Capacitor 99 y/a- 27 signal thereby l time `varying intelligence ysignal voltage 'acrosssaid series circuit arrangement, and means for deriving `an voutput voltage from one of 'said impedances, said output voltage having a magnitude relatively less'than'that of said signal e voltage and lvarying in a predetermined relationship with the impedance value of said photosensitive impedance.

2; A circuit arrangement comprising `a source of time varying intelligence signal voltage, rst and second impedance elements connected in series circuit arrangement at least one of said impedance elements comprising .aphotosensitive impedance, means for impinging light'upon said photosensitive impedance, Emeans 1lor varying the intensity of light impinging on said photosensitive impedance independently of said` source of intelligence signal therebyl varying the impedance value of the said photosensitive impedance, means for applying said time varying intelligence signal voltage across said series circuit arrangement, and means for deriving an loutput voltage from one of said impedances, 'said output voltage `having a magnitude relatively less than that of said signal voltage and varying in a predetermined relationship with the impedance value of said photosensitive impedance.

3. A circuitarrangement comprising a source of time varyingl intelligence signal voltage, rst and second impedance elements connected in series circuit arrangement at least one of said impedance elements comprising a photosensitive impedance, means for impinging light upon4 said photosensitive impedance, means for varying the intensity ofv 1ight impinging on said photosensitive impedance inde endently of said source of intelligence `ying theimpedance value of the said photosensitive pedance, said last-mentioned means comprising movable masking means positioned between said light impinging means and said photosensitive impedance,`means for applying said ltime varying intelligence signal voltage across said series circuit arrangement, and means for deriving an output voltage from one of said impedances, said output voltage having a magnitude relatively less than that of said signal voltagey and varying in a predetermined relationship with the impedance value of said photosensitive impedance.

l4. A circuit arrangement comprising a source of time varying intelligence signal voltage, first and second impedance elements connected inv series circuit arrangement at-'least one vof lsaid impedance elements comprising a photosensitve impedance, means for impinging light4 ,upon said photosensitve impedance, means Vlor varying I the intensity vof light irnpngingon vsaid photosensitve impedance 'independently of ysaid source of vintelligence v signal thereby v,varying theim'pedance value of the said photosensitve f impedance, said last-mentioned means i comprising means Icontrolling the input energy of said light impinging means, rnea'nsv for applying said-time varying intelligence lsignal voltage across said =series circuit arrangement, andmeans for deriving an output voltage.

light source'for impinging light upon said second photo'- sensitive impedance, means for varyingthe intensity of voltage aerossvsaid series circuiti'arrangement, and means lfor :deriving an output voltage from one lof said.photo.

sensitive impedances,said output voltage having wmagnitude relatively less'than thatof said signall voltage and varying' in a predetermined relationship Iwith the im.-

fromone oisaid impedances, said-output voltagehaving a magnitude relatively less than that of said signal voltage and varying in a predetermined relationship Awithjthe yimpedance value of sa'id .photosensitve impedance; l 5.*A creuita'rrangcment comprising a pair of photosensitive impedances connected in series'circuit arrange- 'ment' with each other, means for impinging light upon pedance valuesof--said photosensitve impedances.

A circ-uit arrangementl comprising apair of. photosensitive 4impedances connected in series circuit arrangement with each other, a single light source for impinging j light upony said photosensitve impedances, means'for *varying 'the intensity of lght-impinging on saidphotosaid photosensitve impedances,` means for varying the .intensity o'f light impinging on said photosensitve impedances thereby `varyi'ng'the impedance values of .the said photosensitve impedances, meansv for applying` a signal n v'voltage across'said series circuit arrangement, and means for. derivingfan output-voltage ,froml one of 4said photor sensitive impedances, said output voltage having a magniv tude relatively lessthan thatfof Vsaid signal voltage and' i `varying inl apredetermined relationship with theimpedance `values-ofsaid photosensitive impedances..

' 6. Av circuit arrangement comprising'a 'pair' of photosensitve impedances thereby varying -the impedance values of the said photosensitve impedances, means -for applying a signal voltagev across Asaid seriescircuit arrangement;

2 and meansfor deriving an output voltage from one of said.

photosensitive impedances, said output voltage having a v magnitude relatively less than that ofv said signal voltage and varying in a predetermined relationship with theimpedance values of said photosensitive impedances. v l0. A circuit arrangement comprisinga pair of photo- 'sensitive impedances connected in series circuit arrangesensitive impedances connected in series circuit arrangel -f ment .withl each ,other,'.said photosensitve impedances forming-an integral structure comprising a photosensitve `rna'terial and linear electrodes spaced in atleast three )groups positioned ,on the'lsurface of ysaidfphotosensitive vfrnaterial, said'el'ect'rodes being'jnter-laced with eachother',

.. means `for irnpnging light uponA said `photosensitve impcdl lan'ces, means forvarying the intensity of light impinging 4.on` said fpho'tosensitive,impedances thereby' varying the impedance values of the vsaid photosensitve impedances,

means `for applying va signal voltage across said series circuit arrangement, and means for deriving an output volt- .l age Afrom one of said photosensitve impedances, said'outputvoltage having: a magnitude relatively less than that impedances.

i' 7. .A 'circuit arrangementcompris'ing first -and secondphotosensitve,impedances connected fin seriescircuit arrangement with eachother, a first lightsource Afor impingment' with each other, saidphotosensitve'impedances lforming an integral structure comprising aphotosensitive material and linear electrodes spaced in at least three.-

-groups positioned onthe surface of said photosensitve material, said electrodes being interlaced with each other, asingle light source for impinging light upon said photol sensitive impedances, means for varying the intensity of light'impinging on said photosensitve` impedances thereby varying the impedancevalues of the said photosensitve Ximped'ances; means for applying a signal-.voltage across 45 of said signal voltageand varying in a predetermined relationship withthe impedance values of said photosensitve said series circuit arrangement, and means for derivingan output voltage from one of said photosensitve impedances,

.sa-id output voltage having a magnitude rclativelylessthan'. that of said signal vvoltage and varying in a predetermined relationship with the impedance values of said photosensitve impedances. n

1l.` 'A .circuit arrangement comprising a pair of photosensitive impedances connected inv series circuit arrangement with each other, means for yimpinging light upon y said photosensitve impedances, means for varying the ing light upon said first -photosensitive impedance, a

if second light. source for impinging light upon [said second intensity of light impinging onsaid photosensitve impedances thereby varying the .impedance values of the saidphotosensitive impedances, said last-mentioned means comprising meansjfor increasing the intensity of light irnphotosensitve impedance, .means forvaryin-gthe intensity of light impinging on said first 'photosensitve impedance thereby varying the impedance-value ofthe saidy first phol tosensitive impedance, rneans4 for varyingtheintensityV of light impinging on said-second photosensitve impedance thereby `varying the impedance value ofthe vsaid second photosensitve impedance','means for applying a signal voltage across4 said series circuit arrangement, and 'meansv for deriving an output voltage from one of said photosensitive impedances, said output voltage having a magnitude relatively less than that of said signal voltage and varying in a predetermined relationship with the impedance values ofsaid photosensitve impedances.

Q8. A circuit arrangement comprisingfirst and second vphotosensitve impedances. connected vin series circuit l arrangement with each other, said first and second photosensitive impedances forming an integral structure comprising a` photosensitve material. and linear electrodes spaced in at least three groups positioned on the surface of said photosensitve material, said electrodes being interlaced 'with'each other, a first lightA source for impinging light upon said Vfirst photosensitve impedance, a second pinging on o ne of said photosensitve impedances and simultaneously decreasing the intensity of light impinging on the other of the said photosensitve impedances, means for applying a signal voltage across said series circuit arrangement, and means for deriving an output voltage from one of said photosensitve impedances, said output 60.

voltage having a `magnitude relatively Vless than that of said signal vo` 'ige and varying in a predetermined relal tionship with he impedance values of said photosensitve impedances.

' 12; A circ arrangement comprising first and second photosensitve impedances connected.- in ser-ies circuit arrangement with eaeh other, a first light source for impinging light'upon. said first photosensitve impedance, a second light source for impinging light upon said second photosensitve impedance, potentiometer means controlling-the input energy of said first and second light sources in a manner whereby the intensity of light impinging on` v one of said first and second photosensitve impedances is increased and the intensity of light impinging on thepother of the said first and second photosensitve impedances is simultaneously. decreased,v means for applying a signal 1 ment with each other, a single light source for impinging light` upon said photosensitive impedances, means for varying the intensity of /light impnging onsad photosensitive impedances thereby varying the impedance values rof the said photosensitive impedances, said lastmen-tioned means comprising movable masking means positioned ybetween said light source and said photosensitive impedances in a manner whereby the intensity of light impnging on one of said photosensitive impedances is increased and the intensity of light impnging on the other of saidphotosensitive impedances is simultaneously decreased, means for applying a signal voltage across said series circuit arrangement, and means for deriving an output voltage from one of said photosensitive impedances, said output voltage having a magnitude relatively less than that of said signal voltage and varying in a .predetermined relationship with the impedance values of said photosensitive.impedances."v I l *al 14. A circuit arrangement comprising a-s'ource of time varying signal' intelligence voltage, a firstf'phot'os'ensitive Y impedance,v an impedanceV connected `"infseries circuit 4arrangementl with saidv first photosensitive impedance, ya

second photosensitive impedance, a capacitor connected in series circuit arrangement with said second photosensitiveimpedance, said last-mentioned series circuit arrangement lbeing connected in parallel with said firsftmentioned serie'skciruit arrangement, a single light source for impinginglight upon said` first and second photosensitive impedances, means for varying the lntensity of light impnging on said fir`st"and second photosensitive imi pedances iridependen-tly of saidsources of intelligence signal thereby varying the impedance values of the said first and second photosensitive impedances, said lastmentioned means comprising means for varying the intensity of light impnging on one of said first and second photosensitive impedances in one of an increasing and decreasing direction andrsirnultaneously vvarying the intensity` of light impnging lon theother of the said first and second photosensitive impedances inthe'isame sense, means for applying said time varying intelligence signaly vol-tage across said first and second series circuit arrangemen-ts, and means for deriving an output voltage from said first photosensitive impedance, said output voltage having a magnitude relatively less than that of said signal voltage and varying in a predetermined relationship with the impedance values of said photosensitive impedances.

l5. A circuit arrangement comprising a source of time varying signal intelligence voltage, a first photosensitive impedance, an impedance connected in series circuit arrangement with said first photosensitive impedance, a second photosensitive impedance, said first and second photosensitive impedances forming an in-tegral structure comprising a photosensitive material yand linear electrodes spaced in at least three groups positioned on the surface voli said photosensitive material, said electrodes being interlaced with each other, a capacitor connected in series circuit arrangement with said second photosensitive irnpedance, said last-mentioned series circuit arrangement being connected in parallel with said first-mentioned series circuit arrangement, a single light source for impnging light upon said first and second photosensitive impedances, means for varying the intensity of light impnging on said first and second photosensitive impedances independently of said source of intelligence signal thereby Vvarying the impedance values -of the said first and second photosensitive impedances, said last-mentioned means :comprising means for varying the intensity of light irn- .pinging on one of said first and second photosensitive impedances in one of an increasing and decreasing direction and simultaneously varying the intensi-ty of light impnging on the'other of the said first and second photosensitive impedances in the same sense, means for applying said time varying intelligence signal voltage across said first and second series circuit arrangements, and means for deriving an output voltage from said first photosensitive impedance, said output voltage having a magnitude relatively less than that of said signal-voltage and varying in a predetermined relationship with the impedance values of said photosensitive impedances.

References Cited in the file of this patent UNITED STATES PATENTS 1,602,070 

1. A CIRCUIT ARRANGEMENT COMPRISING A SOURCE OF TIME VARYING INTELLIGENCE SIGNAL VOLTAGE, FISRT AND SECOND IMPEDANCE ELEMENTS CONNECTED IN SERIES CIRCUIT ARRANGEMENT, AT LEAST ONE OF SAID IMPEDANCE ELEMENTS COMPRISING A PHOTOSENSITIVE IMPEDANCE, MEANS FOR IMPINGING RADIATIONS UPON SAID PHOTOSENSITIVE IMPEDANCE, MEANS FOR VARYING THE INTENSITY OF RADIATIONS IMPINGING ON SAID PHOTOSENSITIVE IMPEDANCE INDEPENDENTLY OF SAID SOURCE OF INTELLIGENCE SIGNAL THEREBY VARYING THE IMPEDANCE VALUE OF THE SAID PHOTOSENSITIVE IMPEDANCE, MEANS FOR APLYING SAID TIME VARYING INTELLIGENCE SIGNAL VOLTAGE ACROSSA SAID SERIES CIRCUIT ARRANGMENT, AND MEANS FOR DRIVING AN OUTPUT VOLTAGE FROM ONE OF SAID IMPEDANCES, SAID OUTPUT VOLTAGE HAVING A MAGNITUDE RELATIVELY LESS THAN THAT OF SAID SIGNAL VOLTAGE AND VARYING IN A PREDETERMINED RELATIONSHIP WITH THE IMPEDANCE VALUE OF SAID PHOTOSENSITIVE IMPEDANCE. 